Optical detector and amplifier based on tandem semiconductor devices

Abstract

If a semiconductor device is prepared so that it contains a photoconductive region in electrical series with a photovoltaic region, (i.e., a Schottky barrier or p-n junction) it can function as an optical amplifier and detector. When weak ac light plus an intense dc light are focused on this sample in an appropriate manner, the detected ac electric current will correspond to the intensity of the dc light but have the phase of the ac light; thus a weak ac light signal is effectively amplified, or a dc light signal is converted into an ac electrical signal capable of synchronous detection.

What is claimed is: 
     
       1. A semiconductor device comprising: (a) a photodiode (a region having a photovoltaic junction) region wherein first light of constant magnitude is absorbed;   (b) a photoconductive region electrically connected in series to said junction region, said photoconductive region having a conductivity modulated by absorbed second light having a magnitude which changes with time, and both of said regions having electron affinities so as to not form a barrier to the passage of charge when they are illuminated by said light such that the electrical output from said semiconductor device has a magnitude determined by said constant magnitude and is in phase with said change in magnitude of said second light; and   (c) electrical contacts connected to said photodiode region and said photoconductive region.   
     
     
       2. The semiconductor device of claim 1 wherein said photodiode and said photoconductive region are formed sequentially in tandem so as to be adjacent to each other. 
     
     
       3. The semiconductor device of claim 1 wherein said photodiode and said photoconductive region are connected by an electrically conductive medium. 
     
     
       4. The semiconductor device of claim 2 wherein said photodiode and said photoconductive region include a common semiconductor material. 
     
     
       5. The semiconductor device of claim 4 wherein said photodiode and said photoconductive region include an amorphous semiconductor material. 
     
     
       6. The semiconductor device of claim 5 wherein said amorphous material is selected from the group consisting of silicon, germanium, silicon carbide, silicon nitride and alloys thereof. 
     
     
       7. The semiconductor device of claim 4 wherein said photodiode includes Cu 2  S and CdS and said photoconductive region includes CdS. 
     
     
       8. The semiconductor device of claim 4 wherein said photodiode is a Schottky barrier 
     
     
       9. The semiconductor device of claim 4 wherein said photodiode is a p-n junction. 
     
     
       10. The semiconductor device of claim 1 wherein said photodiode includes a crystalline silicon p-n junction photodiode and said photoconductive region includes a material selected from the group consisting of cadmium-chalcogenides and lead-chalcogenides. 
     
     
       11. The semiconductor device of claim 1 wherein said photodiode includes a material selected from the group consisting of the pnictides of aluminum, gallium and indium in single crystalline form, or alloys thereof.